The present invention relates to a data storage tape cartridge. More particularly, it relates to a hub portion of a data storage tape cartridge.
Data storage tape cartridges have been used for decades in the computer, audio and video fields. While other forms of media storage, such as disk cartridges, are also available, the data storage tape cartridge continues to be an extremely popular form of recording large volumes of information for subsequent retrieval and use. In conjunction with advancements in tape drive and read/write head technology, various improvements in the tape cartridge design have greatly enhanced performance capabilities, while at the same time reducing costs. For example, evolution of magnetic tape media has resulted in storage tapes with increased storage capacity and product longevity. Additionally, the availability of inexpensive plastic materials and production techniques for various tape cartridge components has reduced overall cost. Obviously, to be competitive, data storage tape cartridge manufacturers must not only improve performance of the tape cartridge, but minimize costs whenever possible.
The data storage tape cartridge generally consists of an outer shell or housing maintaining at least one tape reel and a length of magnetic storage tape. The storage tape is wrapped about a hub portion of the tape reel and is driven through a defined tape path by a driving system. The housing normally includes a separate cover and a base, the combination of which creates an opening (or window) of some type for allowing access to the storage tape by a read/write head upon insertion of the data storage tape cartridge into a tape drive. This interaction between storage tape and head may take place within the housing, or the storage tape may be directed away from the housing to an adjacent area at which the read/write head is located. Where the tape cartridge/drive system is designed to provide head-storage tape interface within or very near the housing, tape positioning is extremely important. In this regard, positioning of the storage tape relative to the head is dictated exclusively by a tape path generated within the tape cartridge housing.
Data storage tape cartridges configured for storage tape engagement within the cartridge housing typically employ two tape reels for maintaining the storage tape. The tape path is defined by the location of the tape reels maintaining the storage tape, as well as various tape guides positioned within the housing. Each tape reel is normally rotatably associated with an interior side of the cover, and includes a hub and opposing radial flanges. The storage tape is wrapped around the hub, between the opposing flanges. Generally speaking, with a two-hub (or tape reel) design, the storage tape extends between the two hubs, along the tape guides. The tape guides are strategically positioned within the housing such that at the cartridge window, the storage tape is parallel to a plane of the window.
In addition to facilitating proper positioning of the storage tape at a desired level in the area of the cartridge window, alignment of the tape reels, and in particular the respective hubs, plays a crucial role in minimizing tape wear. Tape reel "alignment" is normally understood to refer to spacing between the hub and the cover (or other section of the housing). If the hub or hubs are not properly spaced relative to the cover, the storage tape will not be optimally positioned along the tape guide(s). More particularly, each tape guide typically includes at least an outer flange against which an edge of the storage tape may abut. The outer flange is necessary to ensure that the storage tape does not "ride off of" or otherwise disengage the tape guide during operation. Where the hubs, and therefore the tape reels, are properly aligned, the storage tape will articulate along the tape guide(s) such that the tape edge does not contact the outer flange. Where at least one of the hubs is not aligned, however, the storage tape will extend from the misaligned tape reel to the tape guide such that the tape edge does in fact contact the outer flange. Over time, this undesirable interaction may lead to wrinkling or other forms of tape deterioration. In other words, a cross-web tension is generated across the storage tape, possibly causing edge wear. Even further, tape reading errors may result at the high tension side of the storage tape. Because current data writing/reading systems make use of nearly the entire width of the storage tape and utilize increasingly smaller data tracks along the storage tape width, it is imperative that every effort be made to ensure proper hub alignment.
One manufacturing method for associating the tape reel within the housing is to first press fit a straight hub pin into one section of the housing, such as the cover. The hub pin is positioned to extend in a generally perpendicular fashion from an interior surface of the cover. The tape reel is then axially received over the hub pin, such as by an axial bore within the hub. The axial bore is slightly larger in diameter than the hub pin, so that the hub can freely rotate about the hub pin. Alternatively, the hub pin is press fitted into a separate base plate element. The base plate element is then secured within the housing (for example to the cover). Once again, the tape reel is disposed over the hub pin via an axial bore within the hub. While this approach is quite viable for mass production, alignment concerns can arise.
For example, while a mechanical press can reproducibly position the hub pin at a desired location and in a desired plane (i.e., perpendicular to the cover or base plate), it is sometimes difficult for this same device to accurately insert the pin to a desired height. In fact, even complex, expensive machinery is not able to produce consistently acceptable hub pin insertion heights. Once again the tape reel is positioned over the hub pin through the axial bore in the hub. The axial bore does not run the entire length of the hub. Instead, the axial bore terminates at an internal, axial thrust surface. Because the hub is normally made by a plastic injection molding process, the length of the axial bore, and thus the position of the axial thrust surface relative to the opposing flanges, is normally constant. When the hub is positioned over the hub pin, the axial thrust surface contacts a leading end of the hub pin. As a result, spacing of the hub relative to the cover or base plate depends solely upon the height of the hub pin. If the hub pin height is greater or less than expected, the hub will not be properly aligned, resulting in the previously described edge wear or errors. Notably, incorrect hub pin height may also occur due to surface variations in the cover or base plate.
In light of the above concern, efforts have been made to inspect the cover or base plate prior to press fitting the hub pin. By inspecting the surface, it was hoped that certain variations or irregularities in the cover or base plate could be compensated for by adjusting the hub pin insertion mechanism. Unfortunately, however, even with rigorous inspection and compensation methods, unacceptable pin height variances may still occur. The press fitting operation is irreversible. Thus, because most tape cartridges are required to maintain a certain tape path with minimal deviation, a hub pin inserted to an unacceptable height normally results in scrapping of the entire assembly. Obviously, this is an extra cost that data storage tape cartridge manufacturers do not wish to incur.
An additional, albeit unrelated, problem with current designs arises due to the interaction between the leading end of the hub pin and the axial thrust surface of the hub. As previously described, the hub is made of plastic. Conversely, the hub pin is normally made of stainless steel. During use, the axial wall is in constant, rotational contact with the leading end of the hub pin. Over time, wearing of the plastic hub at the axial thrust surface may become a prevalent problem, again resulting in hub misalignment.
Data storage tape cartridges are important tools used to maintain vasts amounts of information. However, with increasingly complex writing/reading and magnetic tape technology, design of the data storage tape cartridge must evolve to provide accurate tape positioning within tight tolerances. Further, current marketplace conditions require that the data storage tape cartridge be as inexpensive to manufacture as possible, with little or no scrap. Therefore, a need exists for a cost effective approach to ensuring alignment of a hub within a data storage tape cartridge.